Mesoscale brain dynamics reorganizes and stabilizes during learning

Adaptive behavior is coordinated by neuronal networks that are distributed across multiple brain regions. How cross-regional interactions reorganize during learning remains elusive. We applied multi-fiber photometry to chronically record simultaneous activity of 12-48 mouse brain regions while mice learned a tactile discrimination task. We found that with learning most regions shifted their peak activity from reward-related action to the reward-predicting stimulus. We corroborated this finding by functional connectivity estimation using transfer entropy, which revealed growth and stabilization of mesoscale networks encompassing basal ganglia, thalamus, cortex, and hippocampus, especially during stimulus presentation. The internal globus pallidus, ventromedial thalamus, and several regions in frontal cortex emerged as hub regions. Our results highlight the cooperative action of distributed brain regions to establish goal-oriented mesoscale network dynamics during learning.

Mediodorsal and ventromedial thalamus engage distinct L1 circuits in the prefrontal cortex

SUMMARYInteractions between the thalamus and prefrontal cortex (PFC) play a critical role in cognitive function and arousal. Here we use anatomical tracing, electrophysiology, optogenetics, and 2-photon Ca2+ imaging to determine how ventromedial (VM) and mediodorsal (MD) thalamus target specific cell types and subcellular compartments in layer 1 (L1) of mouse PFC. We find thalamic inputs make distinct connections in L1, where VM engages NDNF+ cells in L1a, and MD drives VIP+ cells in L1b. These separate populations of L1 interneurons participate in different disinhibitory networks in superficial layers by targeting either PV+ or SOM+ interneurons. NDNF+ cells also inhibit the apical dendrites of L5 pyramidal tract (PT) cells, where they suppress AP-evoked Ca2+ signals. Lastly, NDNF+ cells mediate a unique form of thalamus-evoked inhibition at PT cells, selectively blocking VM-evoked dendritic Ca2+ spikes. Together, our findings reveal how two thalamic nuclei differentially communicate with the PFC through distinct L1 micro-circuits.

Artery of percheron infarct: a case report

Artery of Percheron is a part of the posterior circulation occlusion of which is relatively uncommon. It is classically characterised by bilateral infarcts in areas involving the rostral midbrain and/or ventromedial thalamus best seen by a diffusion-weighted imaging (DWI) sequence using MRI. Clinical presentations are variable and include, amnesic impairment, aphasia, dysarthria, ocular movement disorders, motor deficit and cerebellar signs. Our case was a 60-year-old hypertensive and diabetic male with history of alcohol abuse who presented with sudden derangement of sensorium along with restriction of ocular movements and marked cerebellar signs. The diagnosis of werniche encephalopathy suggested initially by the radiologist was rejected because of the acute onset, history of hypertension and marked cerebellar signs which suggested a cerebrovascular accident. Bilateral infarcts with the occlusion of a single artery i.e. artery of percheron which supplies structures bilaterally can easily be confused with werniche encephalopathy which has similar clinical and radiological picture but are managed on different lines. This diagnosis should be kept in mind in drowsy patients with restricted ocular movements and bilateral thalamic and midbrain hyperintensities.